Internal combustion engines with high voltage electrical ignition are usually provided with an ignition coil which provides the high voltage pulses that are needed to produce an electrical spark across the spark gap of a spark plug which, in turn, ignites the compressed fuel-air mixture in the combustion chamber of each cylinder at the start of the power cycle. There are essentially two (2) types of generators for such high voltage pulses, namely the conventional automotive ignition coil which has a primary circuit energized by the engine's low voltage primary power. Another generator for such high voltage pulses is the so-called magneto, which has a rotating armature revolving in a magnetic field, driven by the engine, and which is energized directly from the engine's camshaft or driveshaft. These types of ignition systems have been used successfully for many years, and are described in text books on automotive engineering. One such book is Basic Ignition and Electrical Systems by R. E. Petersen, published by Petersen Publishing Co. and has Library of Congress Catalog Card Number 73-79968.
In those conventional systems using ignition coils or magnetos, the high voltage pulses are generated in a high impedance secondary winding consisting of many turns of fine wire having a resistance of 5 to 10 kilo ohms which produces a high voltage pulse of typically 10 to 15 thousand volts at the instant a current flowing in a primary winding magnetically coupled with the secondary winding is abruptly interrupted. The interruption of the primary current is often done by a set of mechanical contact points, the so-called breaker points which are opened by mechanical cams at precisely timed instants during the rotation of the engine. During recent years, many so-called electronic ignition systems have been developed where the interruption of the primary current is performed by solid state circuit components in order to attain longer life and improved engine performance.
In recent years, there has been increased demand for improvement in engine performance, in regard to fuel efficiency and in regard to reduction of unwanted air-polluting exhaust gas emissions.
In order to attain such improved engine performance, it is desirable to operate engines at a lower fuel to air ratio, a so-called leaner mixture. Ideally, an engine should be operated at a so-called stoichiometric ratio of fuel to air, at which ratio total combustion of the fuel will be attained. Such a ratio, however, is quite lean and is more difficult to ignite and has a decreased flame front velocity compared with the richer conventional fuel-air mixture.
For the above reasons, engine designers have aimed at developing ignition systems that generate more powerful sparks of longer duration than the spark produced by the conventional secondary winding of the ignition coil which, due to its high resistance and high inductance, can only produce a spark of limited intensity and duration. The extended duration of the spark is desirable because combustion chambers are often designed such that a strong swirling motion is imparted to the fuel-air mixture in the combustion chamber, which provides for a more extended contact with the sustained arc of the spark gap.
Many inventors have worked at devising ignition systems that provide such improved spark characteristics as described above. Some of those are listed in the references. One reference in particular, is U.S. Pat. No. 3,919,993, issued Nov. 18, 1975 to J. G. Neuman. That referenced patent describes an ignition system where the spark is generated and sustained by means of two generally parallel connected coordinated power sources such that one of the power sources is very high voltage secondary winding of an ignition coil of generally conventional nature which produces an initial spark across the spark gap at a voltage of sufficient value to safely bridge to spark gap but of a relatively low intensity coordinated with the spark from another ignition coil having a secondary winding which is constructed so as to generate a voltage inpulse of much lower voltae but of a much higher current value. The impulse from the latter ignition coil is timed by appropriate means to happen at a time slightly later than the first initial impulse in a precisely controlled timing sequence.
The present invention discloses an ignition system constructed so as to provide a spark of much increased intensity and increased duration, and such that both the intensity and the duration of the spark can be controlled within wide limits by judicial choice of the controlling components, using two coordinated power sources such that one power source is the secondary winding of a generally conventional ignition coil which produces an initial impulse of voltage high enough to bridge the spark gap with a spark which is generally of low intensity and of short duration coordinated with another power source which will sustain the spark in the form of an electrical arc of high intensity as determined by current limiting circuit elements, and of a duration which is determined by the product of the resistance of the current limiting circuit element and the capacitance of the storage capacitor. Means are provided as required, to ensure that the arc is extinguished after the elapse of such time that it is no longer needed to sustain the combustion in the combustion chamber.
The present invention shows how the two coordinated power sources described above, may be either parallel or series connected.
It is, therefore, a major object of the present invention to provide an improved ignition system for internal combustion engines.
It is an additional object of the present invention to provide an improved ignition system for internal combustion engines which combines a high voltage inductively generated initial impulse of short duration and low current value with a capacitive power source of relatively low voltage, but high current value such as to produce an electric arc of high intensity and extended duration.
It is an additional object of the present invention to provide an improved ignition system for internal combustion engines which combines a high voltage inductively generated initial impulse of short duration and low current value with a capacitive power source of relatively low voltage, but of a high current value such that the two power sources are coordinated in generally parallel connection utilizing high voltage rectifiers such that the high current from the capacitive power souce bypasses the spark distributor.
It is still another object of the present invention to provide an improved ignition system for internal combustion engines which combines a high voltage inductively generated initial impulse of short duration and low current value with a capacitive power source of relatively low voltage, but of a high current value such that the two power sources are combined in generally series connection with at least one high voltage rectifier separating the two power sources.
It is a further object of the present invention to provide an improved ignition system that is generally of simple construction and which provides a spark of such intensity that fouling conditions around the spark gap electrodes will tend to be burned away and in this way contribute to a more reliable ignition system.